Methods of forming graphene-coated diamond particles and polycrystalline compacts

ABSTRACT

Coated diamond particles have solid diamond cores and at least one graphene layer. Methods of forming coated diamond particles include coating diamond particles with a charged species and coating the diamond particles with a graphene layer. A composition includes a substance and a plurality of coated diamond particles dispersed within the substance. An intermediate structure includes a hard polycrystalline material comprising a first plurality of diamond particles and a second plurality of diamond particles. The first plurality of diamond particles and the second plurality of diamond particles are interspersed. A method of forming a polycrystalline compact includes catalyzing the formation of inter-granular bonds between adjacent particles of a plurality of diamond particles having at least one graphene layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/819,031, filed Aug. 5, 2015, now U.S. Pat. No. 9,670,065, issued Jun.6, 2017, which is a divisional of U.S. patent application Ser. No.13/283,021, filed Oct. 27, 2011, now U.S. Pat. No. 9,103,173, issuedAug. 11, 2015, which application claims the benefit of U.S. ProvisionalPatent Application Ser. No. 61/408,382, filed Oct. 29, 2010, titled“Graphene-Coated Diamond Particles, Polycrystalline Compacts, DrillBits, and Compositions of Graphene-Coated Diamond Particles, and Methodsof Forming Same,” the disclosure of each of which is incorporated hereinin its entirety by this reference. The subject matter of thisapplication is also related to the subject matter of U.S. patentapplication Ser. No. 13/166,557, filed Jun. 22, 2011, now U.S. Pat. No.8,840,693, issued Sep. 23, 2014.

FIELD

Embodiments of the present disclosure relate generally to coated diamondparticles, which may be used in, by way of non-limiting example, fluidsuspensions, polymers, elastomers, polycrystalline compacts, andearth-boring tools, and to methods of forming such diamond particles.

BACKGROUND

Diamond crystals are useful in various industrial applications. Forexample, diamond grains may be used in surface polishing, in themanufacture of drill bits, and as conductive filler materials forpolymers and elastomers. Liquid suspensions of diamond grains may beused for lubrication, thermal management, or grinding.

Cutting elements used in earth-boring tools often includepolycrystalline diamond compact (often referred to as “PDC”) cuttingelements, which are cutting elements that include cutting faces of apolycrystalline diamond material. Polycrystalline diamond material ismaterial that includes inter-bonded grains or crystals of diamondmaterial. In other words, polycrystalline diamond material includesdirect, inter-granular bonds between the grains or crystals of diamondmaterial. The terms “grain” and “crystal” are used synonymously andinterchangeably herein.

Polycrystalline diamond compact cutting elements are formed by sinteringand bonding together relatively small diamond grains under conditions ofhigh temperature and high pressure in the presence of a catalyst (forexample, cobalt, iron, nickel, or alloys or mixtures thereof) to form alayer or “table” of polycrystalline diamond material on a cuttingelement substrate. These processes are often referred to ashigh-temperature/high-pressure (or “HTHP”) processes. The cuttingelement substrate may comprise a cermet material (i.e., a ceramic-metalcomposite material) such as cobalt-cemented tungsten carbide. In suchinstances, the cobalt or other catalyst material in the cutting elementsubstrate may diffuse into the diamond grains during sintering and serveas the catalyst material for forming the inter-granulardiamond-to-diamond bonds, and the resulting diamond table, from thediamond grains. In other methods, powdered catalyst material may bemixed with the diamond grains prior to sintering the grains together inan HTHP process. Methods of forming polycrystalline compacts withinterstitial materials are described in U.S. Patent ApplicationPublication No. 2011/0061942 A1, “Polycrystalline Compacts HavingMaterial Disposed in Interstitial Spaces Therein, Cutting Elements andEarth-Boring Tools Including Such Compacts, and Methods of Forming SuchCompacts”, published Mar. 17, 2011, the disclosure of which isincorporated herein in its entirety by this reference.

Upon formation of a diamond table using an HTHP process, catalystmaterial may remain in interstitial spaces between the grains of diamondin the resulting polycrystalline diamond table. The presence of thecatalyst material in the diamond table may contribute to thermal damagein the diamond table when the cutting element is heated during use, dueto friction at the contact point between the cutting element and therock formation being cut.

PDC cutting elements in which the catalyst material remains in thediamond table are generally thermally stable up to a temperature ofabout seven hundred fifty degrees Celsius (750° C.), although internalstress within the cutting element may begin to develop at temperaturesexceeding about four hundred degrees Celsius (400° C.) due to a phasechange that occurs in cobalt at that temperature (a change from the“beta” phase to the “alpha” phase). Also beginning at about four hundreddegrees Celsius (400° C.), there is an internal stress component thatarises due to differences in the thermal expansion of the diamond grainsand the catalyst at the grain boundaries. This difference in thermalexpansion may result in relatively large tensile stresses at theinterface between the diamond grains, and contributes to thermaldegradation of the microstructure when PDC cutting elements are used inservice. Differences in the thermal expansion between the diamond tableand the cutting element substrate to which it is bonded may furtherexacerbate the stresses in the PDC cutting element. This differential inthermal expansion may result in relatively large compressive and/ortensile stresses at the interface between the diamond table and thesubstrate that eventually lead to the deterioration of the diamondtable, cause the diamond table to delaminate from the substrate, orresult in the general ineffectiveness of the cutting element.

Furthermore, at temperatures at or above about seven hundred fiftydegrees Celsius (750° C.), some of the diamond crystals within thediamond table may react with the catalyst material causing the diamondcrystals to undergo a chemical breakdown or conversion to anotherallotrope of carbon. For example, the diamond crystals may graphitize atthe diamond crystal boundaries, which may substantially weaken thediamond table. Also, at extremely high temperatures, in addition tographite, some of the diamond crystals may be converted to carbonmonoxide and/or carbon dioxide.

In order to reduce the problems associated with differences in thermalexpansion and chemical breakdown of the diamond crystals inpolycrystalline diamond cutting elements, so-called “thermally stable”polycrystalline diamond compacts (which are also known as thermallystable products, or “TSPs”) have been developed. Such a thermally stablepolycrystalline diamond compact may be formed by leaching the catalystmaterial (e.g., cobalt) out from interstitial spaces between theinter-bonded diamond crystals in the diamond table using, for example,an acid or combination of acids (e.g., aqua regia). A substantial amountof the catalyst material may be removed from the diamond table, orcatalyst material may be removed from only a portion thereof. Thermallystable polycrystalline diamond compacts in which substantially allcatalyst material has been leached out from the diamond table have beenreported to be thermally stable up to temperatures of about twelvehundred degrees Celsius (1,200° C.). It has also been reported, however,that such fully leached diamond tables are relatively more brittle andvulnerable to shear, compressive, and tensile stresses than arenon-leached diamond tables. In addition, it is difficult to secure acompletely leached diamond table to a supporting substrate. In an effortto provide cutting elements having diamond tables that are morethermally stable relative to non-leached diamond tables, but that arealso relatively less brittle and vulnerable to shear, compressive, andtensile stresses relative to fully leached diamond tables, cuttingelements have been provided that include a diamond table in which thecatalyst material has been leached from a portion or portions of thediamond table. For example, it is known to leach catalyst material fromthe cutting face, from the side of the diamond table, or both, to adesired depth within the diamond table, but without leaching all of thecatalyst material out from the diamond table.

DISCLOSURE

In some embodiments of the disclosure, a coated diamond particle has asolid core comprising diamond and at least one graphene layer over atleast a portion of the solid core.

A method of forming a coated diamond particle includes coating a diamondparticle with a charged species and coating the diamond particle with agraphene layer.

In some embodiments, a composition includes a substance and a pluralityof coated diamond particles dispersed within the substance. Each coateddiamond particle has a diamond core and at least one graphene layerformed or otherwise provided over at least a portion of the diamondcore.

An intermediate structure including a hard polycrystalline materialcomprises a first plurality of diamond particles and a second pluralityof diamond particles. At least one of the first plurality of diamondparticles and the second plurality of diamond particles comprises aplurality of diamond particles having at least one graphene layer. Thefirst plurality of diamond particles and the second plurality of diamondparticles are interspersed.

A method of forming a polycrystalline compact includes coating each of aplurality of diamond particles with at least one graphene layer andcatalyzing the formation of inter-granular bonds between adjacentparticles of the plurality of diamond particles.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming what are regarded as embodiments of thedisclosure, various features and advantages of embodiments of thedisclosure may be more readily ascertained from the followingdescription of some embodiments when read in conjunction with theaccompanying drawings, in which:

FIGS. 1 through 4 illustrate embodiments of coated diamond particles;

FIG. 5 illustrates an embodiment of a polycrystalline diamond compact;

FIG. 6 is a simplified drawing showing how polycrystalline material ofthe polycrystalline diamond compact of FIG. 5 may appear undermagnification, and illustrates inter-bonded larger and smaller grains ofhard material; and

FIG. 7 is a perspective view of an embodiment of a fixed-cutterearth-boring rotary drill bit that includes a plurality ofpolycrystalline diamond compacts like that shown in FIG. 5.

DETAILED DESCRIPTION

The illustrations presented herein are not actual views of anyparticular particles, polycrystalline compact, microstructure ofpolycrystalline material, or drill bit, and are not drawn to scale, butare merely idealized representations employed to describe the presentdisclosure. Additionally, elements common between figures may retain thesame numerical designation.

As used herein, the term “drill bit” means and includes any type of bitor tool used for drilling during the formation or enlargement of awellbore and includes, for example, rotary drill bits, percussion bits,core bits, eccentric bits, bicenter bits, reamers, expandable reamers,mills, drag bits, roller cone bits, hybrid bits, and other drilling bitsand tools known in the art.

As used herein, the term “particle” means and includes any coherentvolume of solid matter having an average dimension of about 2 mm orless. Grains (i.e., crystals) and coated grains are types of particles.As used herein, the term “nanoparticle” means and includes any particlehaving an average particle diameter of about 500 nm or less. The term“nanodiamond” means and includes nanoparticles of diamond material, thatis, diamond grains having an average particle diameter of about 500 nmor less. As used herein, the term “micron diamond” means and includesdiamond grains in a range from about 1 μm to about 500 μm. The term“submicron diamond” means and includes diamond grains in a range fromabout 500 nm to about 1 μm.

The term “polycrystalline material” means and includes any materialcomprising a plurality of grains (i.e., crystals) of the material thatare bonded directly together by inter-granular bonds. The crystalstructures of the individual grains of the material may be randomlyoriented in space within the polycrystalline material.

As used herein, the term “inter-granular bond” means and includes anydirect atomic bond (e.g., covalent, metallic, etc.) between atoms inadjacent grains of material.

As used herein, the term “formed over” means and includes formed on,over, and/or around a material. A material may be formed over (that is,on, over, and/or around) another material by depositing, growing, orotherwise providing a layer of source material on, over, and/or aroundthe another material. The particular process used to deposit each layerwill depend upon the particular material composition of that layer, thecomposition of the another material, the geometry of the anothermaterial and the layer, etc. Many suitable processes for depositing suchlayers are known in the art including, for example, wet chemistryprocesses (e.g., dip coating, solid-gel processes, etc.), physicaldeposition processes (e.g., sputtering, also known as physical vapordeposition (PVD), etc.), and chemical deposition processes (e.g.,chemical vapor deposition (CVD), atomic layer deposition (ALD), etc.),or combinations thereof. In some embodiments, the layer of sourcematerial may be provided over the another material in a fluidized bedreactor, which may also be combined with one or more of theaforementioned techniques.

As used herein, the term “functionalized,” when referring to a surface,means and includes a surface to which a material (i.e., a functionalgroup) has been added by chemical interaction (e.g., bonding). Virtuallyany organic compound may be added to a surface. A surface may befunctionalized to achieve any desired surface property, such ashydrophilicity, hydrophobicity, reactivity with selected chemicalspecies, etc.

FIG. 1 is a simplified cross-section of an embodiment of a coateddiamond particle 100 with a core 102 and an outer layer 106 comprisinggraphene. The core 102 of the coated diamond particle 100 may comprisemicron diamond, submicron diamond, nanodiamond, or any other diamondparticle. The core 102 may be formed by any method known in the art,such as by a detonation synthesis process, commonly used to formnanodiamond. A carbon shell 104, which may be a layer of carbon,commonly referred to in the art as a “carbon onion”, may be formed overthe core 102. The carbon shell 104 may be formed during the formation ofthe core 102 or by heating the core 102 to a high temperature for aperiod of time in which an outer shell of the core 102 may change from acrystalline structure to a non-crystalline structure. For example, thecore 102 may be heated to more than about 800° C., for more than about30 minutes. The carbon shell 104 may be graphite or a graphene-basedstructure. The carbon shell 104 may provide reactive sites to which theouter layer 106 may attach.

The surface of the carbon shell 104 may be chemically modified bycoating it with a charged species, such as a positively chargedamine-terminated group (e.g., a branched-polyethyleneimine (B-PEI)). Thecarbon shell 104 may then be immersed in a solution containing anoppositely charged species (e.g., a polyacrylic acid or a negativelycharged graphene entity). The charged species may be a transientcoating, configured to enable adherence of graphene layers 108. In someembodiments, the charged species may be a permanent coating that becomesintegrated into outer layer 106.

In some embodiments, shown as coated diamond particle 101 in FIG. 2, thecarbon shell 104 may be omitted. The surface of the core 102 may bechemically modified by attaching a reactive group to the core 102, suchas an acid group, an epoxy group, a hydroxyl group, etc. The reactivegroup may provide reactive sites or anchors to which the outer layer 106may attach.

An outer layer 106 may be formed over the core 102 or the carbon shell104 (FIG. 1). The outer layer 106 may comprise graphene layers 108. Thefirst graphene layer 108 (i.e., the graphene layer with the smallestinside diameter) may be formed over the core 102 or the carbon shell104, and each successive graphene layer 108 may be formed over apreviously formed graphene layer 108. The coated diamond particle 100 or101 may be chemically modified by coating it with a charged species. Thecoated diamond particle 100 or 101 may then optionally be immersed in asolution containing an oppositely charged species. A graphene layer 108may then be formed over the charged species or over the oppositelycharged species on the surface of the coated diamond particle 100 or101. The graphene layer 108 may be positively charged, negativelycharged, or uncharged. The process may be repeated any number of times,with graphene layers 108 being formed over a core 102, a carbon shell104, previously formed graphene layers 108, and/or a charged species.Methods of forming graphene layers on substrates are described in U.S.Patent Application Publication No. 2011/0200825 A1, titled“Nano-Coatings for Articles”, published Aug. 18, 2011, the disclosure ofwhich is incorporated herein in its entirety by this reference. Themethods described therein may be used as described herein to applygraphene layers to particles. Methods of depositing nanodiamondlayer-by-layer onto diamond particles have been described in GauravSaini et al., Core-Shell Diamond as a Support for Solid-Phase Extractionand High-Performance Liquid Chromatography, 82 ANAL. CHEM. 4448-56(2010), the disclosure of which is incorporated herein in its entiretyby this reference.

In some embodiments, outer layer 106 may be formed over only a portionof the carbon shell 104, or over only a portion of the core 102. In suchembodiments, a partially coated diamond particle may be formed. In otherembodiments, some graphene layers 108 may be formed over the entirecarbon shell 104 or core 102, while others may be formed over only aportion of the carbon shell 104 or core 102.

Multiple graphene layers 108 may be formed such that the coated diamondparticle 100 or 101 exhibits selected values for one or more selectedphysical properties, such as diameter, thickness of outer layer 106,electrical conductivity, thermal conductivity, mechanical strength,coefficient of thermal expansion, wettability, mass, geometry, surfaceenergy, specific surface area, etc. For example, the specific surfacearea of coated diamond particles 100 or 101 may be from about 10 m²/g toabout 2200 m²/g (as determined by, e.g., a gas adsorption measurement).Coated diamond particles 100 or 101 may have the unique featuresassociated with diamond particles, such as hardness and thermalconductivity, plus features of a graphene coating, such as wettability.When the coated diamond particles 100 or 101 are used in suspensions orsolids, the coated diamond particles 100 or 101 may change some physicalproperties of the suspensions or solids. For example, the thermalconductivity, mechanical strength, and electrical conductivity of afluid or solid may be increased by suspending graphene-coated diamondparticles therein.

Features such as wettability may be particularly valuable in liquids,such as lubricating oils. High thermal conductivity may be an importantfeature for oils used in motors and pumps because, in such applications,heat must be removed from operating components. Diamond particles insuspension, with their high thermal conductivity, may therefore be anattractive additive. Unfortunately, uncoated diamond particles maysettle quickly from oil, because diamond has poor wettability in oil.Rapid settling may make diamond grains impractical for use in oilsbecause the grains must be redispersed to ensure proper lubrication. Inpumps and motors, there may be no convenient way to effect suchredispersion before startup. Graphene may limit the settling problembecause if properly functionalized, it may have higher wettability inoil than diamond does. By coating diamond grains with graphene, thebeneficial features of both materials may be combined. It may bepossible to keep coated diamond particles 100 or 101 in suspension muchlonger than uncoated diamond particles. Because they may remain insuspension, coated diamond particles 100 or 101 may be used effectivelyto increase the thermal conductivity and lubricating properties of theoil.

Coated diamond particles 100 or 101 may also be used for polishing.Diamond crystals have properties that may be beneficial for polishing,such as hardness, thermal conductivity, and durability, but poorwettability may cause uncoated crystals to settle. Functionalizedgraphene coatings may increase wettability of diamond crystals inpolishing liquids, promoting more uniform polishing.

Wettability may also be beneficial in polymers and elastomers. Polymersand elastomers may benefit from higher thermal conductivity of diamondgrains. Diamond grains tend to settle quickly from uncured polymers andelastomers, making it difficult to form a cured product containing agenerally uniform distribution of the diamond grains. Functionalizedgraphene-coated diamond grains, on the other hand, may remain insuspension while the polymer or elastomer cures, resulting in a solidwith diamond grains dispersed uniformly throughout. The thermalconductivity, mechanical strength, and electrical conductivity of thepolymer or elastomer may be increased through the addition ofgraphene-coated diamond particles.

Diamond grains may be used to form cutting elements. For example, asdiscussed with reference to FIG. 5 below, polycrystalline compacts maybe formed by sintering hard polycrystalline materials, including diamondgrains having graphene coatings. To aid bonding of diamond grains in thesintering process, catalysts or other materials may be added among thegrains. Coated diamond particles may be used in the formation ofpolycrystalline compacts. In some embodiments, the coated diamondparticles comprise one or more additional layers of materials other thangraphene for use in a sintering process.

FIG. 3 is a simplified cross section of an embodiment of a coateddiamond particle 120 comprising at least one additional layer 110.Coated diamond particle 120 may, like the coated diamond particle 100shown in FIG. 1, have a core 102 and a carbon shell 104. The carbonshell 104 may optionally be omitted, as in coated diamond particle 121,shown in FIG. 4. Coated diamond particle 120 or 121 may further comprisean outer layer 112 having one or more graphene layers 108 and one ormore additional layers 110. The outer layer 112 of the coated diamondparticle 120 or 121 may comprise alternating graphene layers 108 andadditional layers 110. In some embodiments, the additional layers 110may comprise materials that are catalytic or partially catalytic todiamond synthesis. For example, an additional layer 110 may comprise aGroup VIII A element (e.g., iron, cobalt, or nickel) or an alloythereof. In additional embodiments, the additional layer 110 maycomprise a carbonate material, such as a carbonate of one or more ofmagnesium, calcium, strontium, and barium. The additional layer 110 maycomprise other high-temperature/high-pressure nonmetallic diamondcatalysts, such as silicon. In certain embodiments, an additional layer110 may be a high-pressure activated catalyst such as magnesiumcarbonate. In various embodiments, an additional layer 110 may be aprotective coating of ceramic or refractory metal. Some additionallayers 110 may enhance sustainability of the coated diamond particles120 or 121 in a sintering cycle so that coated diamond particles 120 or121 may remain in their initial state or participate in the HTHPreaction at a later processing stage.

The outer layer 112 of the coated diamond particle 120 may be formedover the carbon shell 104. In embodiments of coated diamond particles121 without a carbon shell 104, the outer layer may be formed directlyover the core 102. The first layer of the outer layer 112 (i.e., thelayer with the smallest inside diameter) may be a graphene layer 108 oran additional layer 110, and may be formed over the core 102 or carbonshell 104. Each successive layer 108 or 110 may be formed over apreviously formed layer 108 or 110. Before forming each graphene layer108 or additional layer 110 over the coated diamond particle 120 or 121,the coated diamond particle 120 or 121 may be chemically modified bycoating it with a charged species, such as those described withreference to the coated diamond particle 100 of FIG. 1. The coateddiamond particle 120 or 121 may then be immersed in a solutioncontaining an oppositely charged species. Multiple graphene layers 108and/or multiple additional layers 110 may be formed such that the coateddiamond particle 120 or 121 exhibits a selected physical property, suchas diameter, thickness of outer layer 112, electrical conductivity,thermal conductivity, mechanical strength, coefficient of thermalexpansion, wettability, mass, geometry surface energy, specific surfacearea, etc. Functionalized graphene-coated diamond grains may mix morefully with micron diamond. Furthermore, graphene layers 108 may providea source of carbon to aid the sintering process.

Additional layers 110 may be formed by depositing, growing, or otherwiseproviding a layer of material. The particular process used to depositeach additional layer 110 may depend upon the particular materialcomposition of that additional layer 110, the composition of thematerial over which it is formed, the geometry of the material overwhich it is formed, etc. Many suitable processes for depositing suchlayers are known in the art including, for example, wet chemistryprocesses (e.g., dip coating, solid-gel processes, etc.), physicaldeposition processes (e.g., PVD) and chemical deposition processes(e.g., CVD, ALD, etc.). In some embodiments, the additional layer 110may be formed in a fluidized-bed reactor.

In some embodiments, the graphene layers 108 may alternate with theadditional layers 110. That is, a graphene layer 108 may be formed overthe core 102 or carbon shell 104, and an additional layer 110 may beformed over the graphene layer 108. A second graphene layer 108 may beformed over the additional layer 110, and a second additional layer 110may be formed over the second graphene layer 108. This sequence maycontinue for any number of layers.

Alternatively, an additional layer 110 may be formed over the core 102or carbon shell 104, and a graphene layer 108 may be formed over theadditional layer 110. A second additional layer 110 may be formed overthe graphene layer 108, and a second graphene layer 108 may be formedover the second additional layer 110. This sequence, too, may continuefor any number of layers.

In other embodiments, multiple graphene layers 108 may be formedsequentially, with additional layers 110 interspersed in patterns otherthan alternating. For example, two, three, four, etc., graphene layers108 may be formed over the core 102 or carbon shell 104, followed by anadditional layer 110. Two, three, four, etc., additional graphene layers108 may be formed, followed by another additional layer 110. Thesequence may continue for any number of layers.

As an additional example, two, three, four, etc., additional layers 110may be formed over the core 102 or carbon shell 104, followed by agraphene layer 108. Two, three, four, etc., additional layers 110 may beformed, followed by another graphene layer 108. The sequence maycontinue for any number of layers.

Similarly, two, three, four, etc., additional layers 110 may be formedover the core 102 or carbon shell 104, followed by two, three, four,etc., graphene layers 108. Two, three, four, etc., additional layers 110may be formed, followed by another two, three, four, etc., graphenelayers 108. The sequence may continue for any number of layers, and thesequence may begin with graphene layers 108 instead of additional layers110. Furthermore, the number of each type of layer need not form anyrecognizable pattern. For example, a single graphene layer 108 could beformed over the core 102 or carbon shell 104, and two, three, four,etc., additional layers 110 could be formed over the graphene layer 108.Two, three, four, etc., additional graphene layers 108 could be formedover the two, three, four, etc., additional layers 110. A singleadditional layer 110 could be formed over the two, three, four, etc.,additional graphene layers 108.

Additional layers 110 need not have the same composition as otheradditional layers 110. In certain embodiments, two or more additionallayers 110 have distinct compositions. For example, a first additionallayer 110 may comprise a metal such as cobalt, iron, nickel, or an alloythereof. A second additional layer 110 may be a high-pressure-activatedcatalyst such as magnesium carbonate. A third additional layer 110 maybe a protective layer of ceramic (e.g., carbides, oxides, etc.) orrefractory metal (e.g., Nb, Ta, Mo, W, Re, Ti, V, Cr, etc.). In otherembodiments, a first additional layer 110 and a second additional layer110 may comprise the same materials, but the materials may havedifferent concentrations in each additional layer 110. In short, layers108 and 110 may be arranged in any combination, configuration, or order,and additional layers 110 may have compositions identical to ordifferent from other additional layers 110 within the outer layer 112.

Due to diamond grains' high strength, the availability of a carbonsource in graphene layers 108, and the processing benefits of additionallayers 110, coated diamond particles 120 or 121 may be particularlyadvantageous in the production of cutting elements of earth-boringtools.

FIG. 5 is a simplified drawing illustrating an embodiment of apolycrystalline compact 130 of the present disclosure that may be formedfrom graphene-coated diamond particles 100, 101, 120, and/or 121. Thepolycrystalline compact 130 includes a table or layer of hardpolycrystalline material 132 that has been provided on (e.g., formed onor secured to) a surface of a supporting substrate 134. In additionalembodiments, the polycrystalline compact 130 may simply comprise avolume of the hard polycrystalline material 132 having any desirableshape. The hard polycrystalline material 132 may be formed from coateddiamond particles 100, 101, 120, and/or 121, described above withreference to FIGS. 1 through 4.

FIG. 6 is an enlarged, schematic view illustrating how a microstructureof the hard polycrystalline material 132 of the polycrystalline compact130 may appear under magnification. As shown in FIG. 6, the grains ofthe hard polycrystalline material 132 may have a multimodal (e.g., abimodal, a trimodal, etc.) grain size distribution. In other embodiments(not shown), the grain size distribution may be monomodal. In multimodalgrain size distributions, the hard polycrystalline material 132 mayinclude a first plurality of grains 136 of hard material having a firstaverage grain size, and at least a second plurality of grains 138 ofhard material having a second average grain size that differs from thefirst average grain size of the first plurality of grains 136. In someembodiments, the hard polycrystalline material 132 may include a thirdplurality of grains (not shown) of hard material, a fourth plurality ofgrains (not shown) of hard material, etc. Polycrystalline compactsformed from multimodal distributions of grains are described more fullyin U.S. Patent Application Publication No. 2011/0031034 A1, titled“Polycrystalline Compacts Including In-Situ Nucleated Grains,Earth-Boring Tools Including Such Compacts, and Methods of Forming SuchCompacts and Tools,” published Feb. 10, 2011, and in U.S. patentapplication Ser. No. 13/208,989, now U.S. Pat. No. 8,985,248, issuedMar. 24, 2015, titled “Cutting Elements Including Nanoparticles in atLeast One Portion Thereof, Earth Boring Tools Including Such CuttingElements, and Related Methods,” filed Aug. 12, 2011, the disclosure ofeach of which is incorporated herein in its entirety by this reference.Embodiments described therein may be practiced using the coated diamondparticles 100, 101, 120, and/or 121. As a non-limiting example, a PDCcutting element may have two or more layers, and each layer may compriseone or more of coated diamond particles 100, 101, 120, and/or 121. Insuch embodiments, the two or more layers may comprise coated diamondparticles 100, 101, 120, and/or 121 of differing sizes and/orcompositions.

In the examples that follow, though only two pluralities of grains 136and 138 are discussed, additional pluralities of grains may be used. Asone example, the first plurality of grains 136 may be formed from coateddiamond particles 120 or 121 formed from nanodiamond cores 102, and thesecond plurality of grains 138 may be formed from coated diamondparticles 120 or 121 formed from micron diamond cores 102. Thus, thefirst plurality of grains 136 may be formed from nanoparticles used toform the microstructure of the hard polycrystalline material 132.

A large difference between the average grain size of the first pluralityof grains 136 and the average grain size of the second plurality ofgrains 138 may result in smaller interstitial spaces or voids within themicrostructure of the hard polycrystalline material 132 (relative toconventional polycrystalline materials), and the total volume of theinterstitial spaces or voids may be more evenly distributed throughoutthe microstructure of the hard polycrystalline material 132 (relative toconventional polycrystalline materials). As a result, any material thatmight be present within the interstitial spaces (such as material ofadditional layers 110 formed over nanodiamond cores 102) may also bemore evenly distributed throughout the microstructure of the hardpolycrystalline material 132 within the relatively smaller interstitialspaces therein.

In some embodiments, the hard polycrystalline material 132 may include acatalyst material 140 (shaded black in FIG. 6) disposed in interstitialspaces between the first plurality of grains 136 and the secondplurality of grains 138. The catalyst material 140 may comprise acatalyst capable of forming (and used to catalyze the formation of)inter-granular bonds between the first plurality of grains 136 and thesecond plurality of grains 138 of the hard polycrystalline material 132.In other embodiments, however, the interstitial spaces between the firstplurality of grains 136 and the second plurality of grains 138 in someregions of the hard polycrystalline material 132, or throughout theentire volume of the hard polycrystalline material 132, may be at leastsubstantially free of such a catalyst material 140. In such embodiments,the interstitial spaces may comprise voids filled with gas (e.g., air),or the interstitial spaces may be filled with another material that isnot a catalyst material and that will not contribute to degradation ofthe polycrystalline material 132 when the compact 130 is used in adrilling operation.

The catalyst material may be formed of materials that may be included inone or more additional layers 110. For example, the catalyst material140 may comprise a Group VIII A element or an alloy thereof, and thecatalyst material 140 may comprise between about 0.1% and about 20% byvolume of the hard polycrystalline material 132. In additionalembodiments, the catalyst material 140 may comprise a carbonatematerial, such as a carbonate of one or more of magnesium, calcium,strontium, and barium. Carbonates may also be used to catalyze theformation of polycrystalline diamond.

The hard polycrystalline material 132 of the compact 130 may be formedusing an HTHP process. Such processes, and systems for carrying out suchprocesses, are generally known in the art and not described in detailherein. In accordance with some embodiments of the present disclosure,the first plurality of grains 136 may be nucleated in situ during theHTHP process used to form the hard polycrystalline material 132, asdescribed in U.S. Patent Application Publication No. 2011/0031034 A1,previously incorporated by reference. In embodiments in which the firstplurality of grains 136 is formed from coated diamond particles 100,101, 120, and/or 121, graphene layers 108 may act as carbon-richcenters, and, optionally, additional layers 110 may catalyze in situdiamond formation during HTHP processing.

In some embodiments, the hard polycrystalline material 132 may be formedover a supporting substrate 134 (as shown in FIG. 5) of cementedtungsten carbide or another suitable substrate material in aconventional HTHP process of the type described, by way of non-limitingexample, in U.S. Pat. No. 3,745,623, titled “Diamond Tools forMachining,” issued Jul. 17, 1973, or may be formed as a freestandingpolycrystalline compact (i.e., without the supporting substrate 134) ina similar conventional HTHP process as described, by way of non-limitingexample, in U.S. Pat. No. 5,127,923, titled “Composite Abrasive CompactHaving High Thermal Stability,” issued Jul. 7, 1992, the disclosure ofeach of which is incorporated herein in its entirety by this reference.In some embodiments, the catalyst material 140 may be supplied from thesupporting substrate 134 during an HTHP process used to form the hardpolycrystalline material 132. For example, the substrate 134 maycomprise a cobalt-cemented tungsten carbide material. The cobalt of thecobalt-cemented tungsten carbide may serve as the catalyst material 140during the HTHP process. In some embodiments, the catalyst material 140may be supplied by one or more additional layers 110 of coated diamondparticles 120 or 121. In other words, one or more additional layers 110of coated diamond particles 120 or 121 may comprise the catalystmaterial 140.

To form the hard polycrystalline material 132 in an HTHP process, aparticulate mixture comprising grains of hard material, such as coateddiamond particles 100, 101, 120, and/or 121, described with reference toFIGS. 1 through 4, may be subjected to elevated temperatures (e.g.,temperatures greater than about 1,000° C.) and elevated pressures (e.g.,pressures greater than about 5.0 gigapascals (GPa)) to forminter-granular bonds between the particles, thereby forming the hardpolycrystalline material 132. Coated diamond particles 100, 101, 120,and/or 121 may provide graphene layers 108 as a source of carbon, whichmay promote enhanced sintering of diamond-to-diamond bonds. Coateddiamond particles 100, 101, 120, and/or 121 may be used in conjunctionwith the methods described in U.S. Patent Application Publication No.2011/0031034 A1, previously incorporated by reference. Specifically,various non-diamond nanoparticles may act as a source for diamondnucleation in situ under the appropriate sintering conditions. In someembodiments, the particulate mixture may be subjected to a pressuregreater than about six gigapascals (6.0 GPa) and a temperature greaterthan about 1,500° C. in the HTHP process.

The overall polycrystalline microstructure that may be achieved inaccordance with embodiments of the present disclosure may result inpolycrystalline diamond compacts that exhibit improved durability,conductivity, and/or thermal stability.

Polycrystalline compacts that embody teachings of the presentdisclosure, such as the polycrystalline compact 130 illustrated in FIG.5, may be formed and secured to drill bits for use in forming wellboresin subterranean formations. As a non-limiting example, FIG. 7illustrates a fixed-cutter type earth-boring rotary drill bit 150 thatincludes a plurality of polycrystalline compacts 130 as previouslydescribed herein. The rotary drill bit 150 includes a bit body 152, andthe polycrystalline compacts 130, which serve as cutting elements, arebonded to the bit body 152. The polycrystalline compacts 130 may bebrazed or otherwise secured within pockets formed in the outer surfaceof the bit body 152. Polycrystalline compacts that embody teachings ofthe present disclosure may be formed and secured to any other type ofearth-boring tool for use in forming wellbores in subterraneanformations.

Additional non-limiting example embodiments of the disclosure aredescribed below.

Embodiment 1

A coated diamond particle comprising a solid core comprising diamond,and at least one graphene layer over at least a portion of the solidcore.

Embodiment 2

The coated diamond particle of Embodiment 1, further comprising at leastone additional layer formed over at least a portion of the solid core.

Embodiment 3

The coated diamond particle of Embodiment 2, wherein the at least onegraphene layer comprises two or more graphene layers separated by the atleast one additional layer.

Embodiment 4

The coated diamond particle of Embodiment 2, wherein the at least oneadditional layer comprises two or more additional layers separated bythe at least one graphene layer.

Embodiment 5

The coated diamond particle of any of Embodiment 1 through Embodiment 4,further comprising a carbon shell.

Embodiment 6

The coated diamond particle of any of Embodiment 1 through Embodiment 5,wherein the coated diamond particle has a diameter of about 500 nm orless.

Embodiment 7

A method of forming a coated diamond particle, comprising coating adiamond particle with a charged species and coating the diamond particlewith a graphene layer.

Embodiment 8

The method of Embodiment 7, further comprising coating the diamondparticle with a material selected from the group consisting of groupVIII A elements and alloys thereof.

Embodiment 9

The method of Embodiment 7, further comprising immersing the diamondparticle in a solution comprising an oppositely charged species beforecoating the diamond particle with a graphene layer.

Embodiment 10

A composition comprising a substance and a plurality of coated diamondparticles dispersed within the substance. Each coated diamond particlehas a diamond core and at least one graphene layer formed over at leasta portion of the diamond core.

Embodiment 11

The composition of Embodiment 10, wherein the substance comprises afluid. The coated diamond particles are suspended in the fluid.

Embodiment 12

The composition of Embodiment 10, wherein the substance comprises asolid material. The coated diamond particles are dispersed throughoutthe solid material.

Embodiment 13

An intermediate structure including a hard polycrystalline materialcomprising a first plurality of diamond particles and a second pluralityof diamond particles. At least one of the first plurality of diamondparticles and the second plurality of diamond particles comprises aplurality of diamond particles having at least one graphene layer. Thefirst plurality of diamond particles and the second plurality of diamondparticles are interspersed.

Embodiment 14

The intermediate structure of Embodiment 13, wherein the first pluralityof diamond particles has a first average diameter and the secondplurality of diamond particles has a second average diameter differentfrom the first average diameter.

Embodiment 15

The intermediate structure of Embodiment 13 or Embodiment 14, furthercomprising a catalyst material disposed in interstitial spaces betweenthe first plurality of diamond particles and the second plurality ofdiamond particles.

Embodiment 16

The intermediate structure of any of Embodiment 13 through Embodiment15, wherein at least one of the first plurality of diamond particles andthe second plurality of diamond particles comprises a plurality ofdiamond particles having at least one layer comprising a materialselected from the group consisting of cobalt, iron, nickel, and alloysthereof.

Embodiment 17

The intermediate structure of any of Embodiment 13 through Embodiment16, wherein at least one of the first plurality of diamond particles andthe second plurality of diamond particles comprises a plurality ofdiamond particles having at least one layer comprising magnesiumcarbonate.

Embodiment 18

The intermediate structure of any of Embodiment 13 through Embodiment17, wherein at least one of the first plurality of diamond particles andthe second plurality of diamond particles comprises a plurality ofdiamond particles having at least one layer comprising a materialselected from the group consisting of ceramics and refractory metals.

Embodiment 19

The intermediate structure of any of Embodiment 13 through Embodiment18, further comprising a first layer and a second layer. The first layerand the second layer each comprise a plurality of diamond particleshaving at least one graphene layer. The plurality of diamond particlesof the first layer has a different average diameter from an averagediameter of the plurality of diamond particles of the second layer.

Embodiment 20

A method of forming a polycrystalline compact, comprising coating eachof a plurality of diamond particles with at least one graphene layer andcatalyzing the formation of inter-granular bonds between adjacentparticles of the plurality of diamond particles.

Embodiment 21

The method of Embodiment 20, further comprising coating each of theplurality of diamond particles with at least one additional layer.

The foregoing description is directed to particular embodiments for thepurpose of illustration and explanation. It will be apparent to oneskilled in the art that many modifications and changes to theembodiments set forth above are possible without departing from thescope of the embodiments disclosed herein as hereinafter claimed,including legal equivalents. It is intended that the following claims beinterpreted to embrace all such modifications and changes.

What is claimed is:
 1. A method of forming a polycrystalline compact,comprising: forming at least two graphene layers separated by at leastone additional layer of material on each of a first plurality of diamondparticles; and catalyzing the formation of inter-granular bonds betweenadjacent particles of the first plurality of diamond particles.
 2. Themethod of claim 1, further comprising interspersing the first pluralityof diamond particles with a second plurality of diamond particles. 3.The method of claim 2, wherein the first plurality of diamond particleshas a first average diameter and the second plurality of diamondparticles has a second average diameter different from the first averagediameter.
 4. The method of claim 2, further comprising disposing acatalyst material in interstitial spaces between the first plurality ofdiamond particles and the second plurality of diamond particles.
 5. Themethod of claim 2, wherein at least one of the first plurality ofdiamond particles and the second plurality of diamond particlescomprises a plurality of diamond particles having at least one layercomprising a material selected from the group consisting of cobalt,iron, nickel, and alloys thereof.
 6. The method of claim 2, wherein atleast one of the first plurality of diamond particles and the secondplurality of diamond particles comprises a plurality of diamondparticles having at least one layer comprising magnesium carbonate. 7.The method of claim 2, wherein at least one of the first plurality ofdiamond particles and the second plurality of diamond particlescomprises a plurality of diamond particles having at least one layercomprising a material selected from the group consisting of ceramics andrefractory metals.
 8. The method of claim 1, further comprising:providing a first volume comprising the first plurality of diamondparticles; providing a second volume comprising a second plurality ofdiamond particles having at least one graphene layer, wherein the secondplurality of diamond particles has a different average diameter from anaverage diameter of the first plurality of diamond particles; andcatalyzing the formation of inter-granular bonds between adjacentparticles of the second plurality of diamond particles.
 9. The method ofclaim 1, further comprising suspending the first plurality of diamondparticles in a fluid.
 10. The method of claim 1, wherein the firstplurality of diamond particles comprises diamond nanoparticles, themethod further comprising mixing the diamond nanoparticles withnon-diamond nanoparticles.
 11. The method of claim 10, furthercomprising nucleating diamond in situ on the non-diamond nanoparticles.12. The method of claim 1, wherein forming the at least two graphenelayers on each of a first plurality of diamond particles comprisescoating diamond nanoparticles with the at least two graphene layers. 13.The method of claim 1, wherein forming the at least one additional layeron each of the first plurality of diamond particles comprises at leastone process selected from the group consisting of wet chemistryprocesses, physical deposition processes, and chemical depositionprocesses.
 14. The method of claim 1, wherein forming the at least oneadditional layer on each of the first plurality of diamond particlescomprises coating the diamond particles in a fluidized-bed reactor. 15.The method of claim 1, wherein forming the at least one additional layeron each of the first plurality of diamond particles comprises coatingthe diamond particles with at least one material selected from the groupconsisting of Group VIII A metals, carbonates, ceramics, and refractorymetals.
 16. A method of forming a polycrystalline compact, comprising:forming a first plurality of coated diamond particles, wherein eachcoated diamond particle comprises at least two graphene layers separatedby at least one additional layer comprising a material selected from thegroup consisting of cobalt, iron, nickel, niobium, tantalum, molybdenum,tungsten, rhenium, titanium, vanadium, chromium, silicon, carbonates,carbides, and oxides; and subjecting the first plurality of coateddiamond particles to a high-temperature high-pressure process.
 17. Themethod of claim 16, wherein each coated diamond particle comprises atleast two additional layers separated by at least one graphene layer ofthe at least two graphene layers.
 18. The method of claim 16, subjectingthe first plurality of coated diamond particles to an HTHP processcomprises subjecting the coated diamond particles to a pressure greaterthan about 5.0 GPa and a temperature greater than about 1,000° C. 19.The method of claim 1, wherein the first plurality of diamond particlesfurther comprise loose diamond particles.
 20. The method of claim 16,wherein the first plurality of diamond particles further comprise loosediamond particles.